29,270 research outputs found
Charmonium properties in hot quenched lattice QCD
We study the properties of charmonium states at finite temperature in
quenched QCD on large and fine isotropic lattices. We perform a detailed
analysis of charmonium correlation and spectral functions both below and above
. Our analysis suggests that both S wave states ( and )
and P wave states ( and ) disappear already at about . The charm diffusion coefficient is estimated through the Kubo formula and
found to be compatible with zero below and approximately at
.Comment: 32 pages, 19 figures, typo corrected, discussions on isotropic vs
anisotropic lattices expanded, published versio
A non-perturbative estimate of the heavy quark momentum diffusion coefficient
We estimate the momentum diffusion coefficient of a heavy quark within a pure
SU(3) plasma at a temperature of about 1.5Tc. Large-scale Monte Carlo
simulations on a series of lattices extending up to 192^3*48 permit us to carry
out a continuum extrapolation of the so-called colour-electric imaginary-time
correlator. The extrapolated correlator is analyzed with the help of
theoretically motivated models for the corresponding spectral function.
Evidence for a non-zero transport coefficient is found and, incorporating
systematic uncertainties reflecting model assumptions, we obtain kappa = (1.8 -
3.4)T^3. This implies that the "drag coefficient", characterizing the time
scale at which heavy quarks adjust to hydrodynamic flow, is (1.8 - 3.4)
(Tc/T)^2 (M/1.5GeV) fm/c, where M is the heavy quark kinetic mass. The results
apply to bottom and, with somewhat larger systematic uncertainties, to charm
quarks.Comment: 18 pages. v2: clarifications adde
Vector screening masses in the quark-gluon plasma and their physical significance
Static and non-static thermal screening states that couple to the conserved
vector current are investigated in the high-temperature phase of QCD. Their
masses and couplings to the current are determined at weak coupling, as well as
using two-flavor lattice QCD simulations. A consistent picture emerges from the
comparison, providing evidence that non-static Matsubara modes can indeed be
treated perturbatively. We elaborate on the physical significance of the
screening masses.Comment: 4 pages, 3 figures. Submitted as a contribution to the proceedings of
the Quark Matter 2014 conference (talk given by H. Meyer
Critical point and scale setting in SU(3) plasma: An update
We explore a method developed in statistical physics which has been argued to
have exponentially small finite-volume effects, in order to determine the
critical temperature Tc of pure SU(3) gauge theory close to the continuum
limit. The method allows us to estimate the critical coupling betac of the
Wilson action for temporal extents up to Nt ~ 20 with < 0.1% uncertainties.
Making use of the scale setting parameters r0 and sqrt{t0} in the same range of
beta-values, these results lead to the independent continuum extrapolations Tc
r0 = 0.7457(45) and Tc sqrt{t0} = 0.2489(14), with the latter originating from
a more convincing fit. Inserting a conversion of r0 from literature
(unfortunately with much larger errors) yields Tc / LambdaMSbar = 1.24(10).Comment: 12 pages. v2: clarifications and references added, published versio
Deformation mechanics of deep surface flaw cracks
A combined analytical and experimental program was conducted to determine the deformation characteristics of deep surface cracks in Mode I loading. An approximate plane finite element analysis was performed to make a parameter study on the influence of crack depth, crack geometry, and stress level on plastic zones, crack opening displacement, and back surface dimpling in Fe-3Si steel and 2219-T87 aluminum. Surface replication and profiling techniques were used to examine back surface dimple configurations in 2219-T87 aluminum. Interferometry and holography were used to evaluate the potential of various optical techniques to detect small surface dimples on large surface areas
Young people's attitudes to religious diversity : quantitative approaches from social psychology and empirical theology
This essay discusses the design of the quantitative component of the ‘Young People’s Attitudes to Religious Diversity’ project, conceived by Professor Robert Jackson within the Warwick Religions and Education Research Unit, and presents some preliminary findings from the data. The quantitative component followed and built on the qualitative component within a mixed method design. The argument is advanced in seven steps: introducing the major sources of theory on which the quantitative approach builds from the psychology of religion and from empirical theology; locating the empirical traditions of research among young people that have shaped the study; clarifying the notions and levels of measurement employed in the study anticipating the potential for various forms of data analysis; discussing some of the established measures incorporated in the survey; defining the ways in which the sample was structured to reflect the four nations of the UK, and London; illustrating the potential within largely descriptive cross-tabulation forms of analysis; and illustrating the potential within more sophisticated multivariate analytic models
A relation between screening masses and real-time rates
Thermal screening masses related to the conserved vector current are
determined for the case that the current carries a non-zero Matsubara
frequency, both in a weak-coupling approach and through lattice QCD. We point
out that such screening masses are sensitive to the same infrared physics as
light-cone real-time rates. In particular, on the perturbative side, the
inhomogeneous Schrodinger equation determining screening correlators is shown
to have the same general form as the equation implementing LPM resummation for
the soft-dilepton and photon production rates from a hot QCD plasma. The static
potential appearing in the equation is identical to that whose soft part has
been determined up to NLO and on the lattice in the context of jet quenching.
Numerical results based on this potential suggest that screening masses
overshoot the free results (multiples of 2piT) more strongly than at zero
Matsubara frequency. Four-dimensional lattice simulations in two-flavour QCD at
temperatures of 250 and 340 MeV confirm the non-static screening masses at the
10% level. Overall our results lend support to studies of jet quenching based
on the same potential at T > 250 MeV.Comment: 32 pages. v2: clarifications added, typos corrected; published
versio
Narrow Band Gap Semiconductors as Acoustic Phonon Transducers
It \u27s actually with some considerable apprehension that I address this audience. I will try to alleviate my apprehension somewhat by telling you right at the outset that I do not have a single data slide showing a detected flaw. What\u27s more I have to confess, I have never detected a flaw. I sincerely hope you\u27ll forgive me for this. My apprehension is heightened by my observation over the last several days that there is very little interest in ultrasonic work at the frequencies that are of interest to me, the range of about 1 to 10 GHz. I don\u27t think I\u27ve heard anything over 1 GHz mentioned. Perhaps it\u27s becoming apparent to most of you that I am not principally in nondestructive evaluation. What I am interested in is lattice dynamics; more specifically relaxation effects in dielectric solids
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